FIGS. 4 to 6 are schemes for explaining a prior art example, in which FIG. 4 is a cross sectional side view showing schematically a magnetic rotation sensor; FIG. 5 is a graph showing a characteristic curve indicating the relation between the gap between an MR sensor and a magnetic rotating drum and the sensor output; and FIG. 6 is an exploded perspective view of the principal part showing the gap adjusting mechanism.
In the figures, reference numeral 1 is a shaft mounted on a housing 2, perpendicularly thereto and the magnetic rotating drum 3 is supported by the shaft/rotatably and positioned. 4 is a guide, which is molded, consisting of a bottom plane 4a and a vertical plane 4b. On the lower surface of the bottom plane 4a there are disposed mounting portions 5 having a small diameter. The mounting portions 5 are movable in slits 6 formed in the housing 2, extending towards the magnetic rotating drum 2. 7 is the MR sensor mounted on the vertical plane 4b of the guide 4 described above, which detects the rotational direction and the rotating speed of the magnetic rotating drum 3 and which is so constructed that the output thereof is led out to the exterior through a wiring film F. Further 9 is a hole for positioning the magnetic rotating drum 3.
The gap G between the MR sensor 7 and the magnetic rotating drum 3 is determined by the diameter of the magnetic rotating drum 3, the thickness of the MR sensor 7, the position of the guide 4, etc. and fluctuations in the precision of the gap G are determined by fluctuation of a plurality of elements as described above, combined with each other.
If the fluctuations in the gap G described above are in a tolerance region A as indicated in FIG. 5, the sensor 7 can obtain an output higher than a required value B. On the contrary, in the case where they are not in the tolerance region A, it is not possible to obtain any required sensor output.
In this case, adjustment was effected by moving the mounting portions 5 of the guide 4 in the slits 6.
However, since the slits are set previously so as to have a clearance between the mounting portions 5 of the guide and the periphery thereof, the guide 4 can be slightly inclined at securing it by means of nuts 8. Therefore the adjustment was difficult for this reason and others.